This invention relates to rotary filters.
Rotary filters are used for efficient, cost-effective liquid-solids separation in many areas such as chemical, pharmaceutical, food processing and fuel/metallurgical industries.
Rotary vacuum filters typically include a perforated drum whose interior is maintained under vacuum. The drum rotates through a liquid/solid suspension and liquids and gases are drawn into the interior of the drum with the solids forming a cake on the exterior surface of the drum. The cake is discharged by a blowback valve or shoe fitted with very close clearances to the accurately machined inside surface of the cylinder. Gas such as air is forced through the blowback valve so as to effect removal of the cake. As will be appreciated by those skilled in the art, it is essential that the clearance between the blowback valve and the interior of the drum be maintained at the close design tolerance so that gas discharged through the blowback valve does not enter the interior of the drum which would degrade the vacuum and decrease the performance of the filter.
In prior art rotary filters, the blowback valves are generally composed of cast or fabricated machined segments which are mechanically fastened to each other with nuts and bolts and connected to a source of pressurized air. The clearance between the blowback valve and interior of the drum was adjusted in the prior art by loosening the bolting and jacking one or more of the segments in or out to adjust the running clearance between the blowback valve and inside diameter of the filter drum. This operation of necessity was performed through access hatches in an end face of the drum. That is, a service technician would reach or climb inside the drum through the access hatch to loosen the securing bolts and to retighten them after the blowback valve was jacked to the appropriate clearance. Since this operation had to be performed from either end of the filter unless the technician climbed inside, the maximum length of the filter was constrained to be on the order of four feet so that no valve was more than two feet from either end of the drum.
It is known that it is more cost-effective to increase the length of a rotary filter so as to increase the surface area of the drum as opposed to increasing drum diameter. Heretofore, however, it was not practical to increase the length of the drum because of the necessity of a technician reaching or climbing inside and performing the blowback valve adjustment. As will be seen hereinbelow, the present invention allows a rotary filter to be longer, and therefore, more cost-effective, than rotary filters known in the prior art.